I. Field of the Invention
The present invention relates generally to gear pumps, and more particularly, to gear pumps which are hydrostatically balanced.
II. Description of the Prior Art
In a gear pump, fluid is carried from an inlet port through a pumping chamber to an outlet port by a pair of meshed gears comprising a drive gear and a driven gear. Fluid enters the pumping chamber via filling a partial vacuum formed near the inlet port by unmeshing of the gear teeth. The fluid is carried in spaces formed between the gear teeth and the pumping chamber. The fluid is forced out of the pumping chamber and through the outlet port as the gears go back into mesh. Usually forces imposed upon the gears are substantially unbalanced. Included are forces due to increasing pressure of fluid moving around the pumping chamber toward the outlet port as well as any excess pressure formed by trapping or compression of fluid between meshing teeth. Also included are reaction forces proportional to drive torque imposed upon the driven gear by the drive gear. Because of these unbalanced forces, drive and driven gears of prior art gear pumps are generally provided with shafts supported by bearings on each side. Fabrication of such an assembly is expensive because of the accuracies required in providing necessary alignment of the various bearings, shafts and mechanical parts used in defining the pumping chambers.
It is known, as disclosed by Schwartz and Grafstern in Pictorial Handbook of Technical Devices, Chemical Publishing Co., Inc., New York, 1971, to provide pressure balancing fluid paths from the inlet port to first opposing chamber segments and the outlet port to second opposing chamber segments through first and second pairs of passages in the housing, respectively. However, such an arrangement does not completely balance the pressure imbalances and does not address the reaction forces at all. Accordingly, it is still necessary to utilize shafts and bearings to support the gears. Further, the first and second pairs of passages result in an enlarged housing that is more expensive to fabricate.